Session mobility means transfer of a session performed via a first network to a second network when a terminal is required to change its access to the second network from a current first network due to a change of a geographical position while performing the session with an external entity via the first network. As such, the transfer of the session without discontinuity is referred to as session continuity.
The session continuity may be implemented, for example, by allowing a terminal being performing a session via a WLAN to perform the session via a UTRAN/GERAN when the terminal is moved to the UTRAN/GERAN due to a change of a geographical position or the like.
The session continuity will be described in detail with reference to FIG. 1 hereafter.
FIG. 1 is an exemplary view showing session continuity in accordance with the related art. Referring to FIG. 1, a UE-a is located in coverage of a WLAN and performs a session with a UE-b for sending of voice data and non-voice data via the WLAN (S11).
Hereafter, the UE-a geographically moves to coverage of a UTRAN/GERAN (S12).
The UE-a sends a CS SETUP message to an MGCF via a CS domain of the UTRAN/GERAN so as to maintain the session for voice even if the UE-a is to be located in the coverage of the UTRAN/GERAN (S13).
The MGCF receives the CS SETUP message and then sends an INVITE request having a VDN as a URI (INVITE R-URI=VDN) to an application server (AS) (S14).
The application server (AS) receives the message and then sends a re-INVITE to the UE-b so as to re-establish the session for voice with the UE-b (S15).
Likewise, the UE-a sends the INVITE request having a VDI as the URI (ex., INVITE R-URI=VDI) together with a Replaces header to the application server (AS) so as to maintain the session for non-voice data even if the UE-a is to be located in the coverage of the UTRAN/GERAN (S16).
The application server (AS) receives the message and then sends a re-INVITE to the UE-b so as to re-establish the session for non-voice data with the UE-b (S17).
By the procedures, the UE-a can continuously maintain the session with the UE-b.
In the aforementioned related art, the session continuity is supported only when the terminal is geographically moved. That is, in the related art, the session continuity is supported only when a radio environment of the terminal is changed or a usable radio resource thereof is changed.
However, the aforementioned related art cannot propose a solution for a case that a first network is required to be temporarily stopped due to maintenance by a service operator or a case that terminals are required to be moved to a second network due to a load balancing or the like.
Also, the aforementioned related art has a drawback that it supports session transfer regardless of a terminal user's intention. That is, in case that the second network charges more, the session is transferred regardless of the user's intention. Else, there is another drawback that whether or not the session transfer is supported depends on a manufacturer of a terminal or a service operator.